The present invention relates to semiconductors, specifically to semiconductor bodies and devices comprising layers or zones consisting of different semiconductor materials.
A known high frequency metal-semiconductor field-effect transistor (MES-FET) comprises a semiconductor substrate made of gallium arsenide GaAs onto which a thin (e.g. 0.5 microns) epitaxial layer of gallium arsenide is formed which is relatively heavy doped with a donor material (about 1.times.10.sup.17 donor atoms per cubic centimeter). The doped epitaxial layer is provided with source and drain contacts, and the portion of the layer between these contacts operates as channel of controllable conductivity. The device further comprises a gate electrode in form of a Schottky contact which is provided on the channel and enables to control the resistance of the channel by carrier depletion. MES-FET devices and other applications of heterostructure-semiconductor bodies are disclosed in the magazine "Journal of the Electrochemical Soceity", December 1978, pp. 478C to 499C.
It is also known to form the doped channel layer of a field-effect transistor of this type in high-resistivity gallium arsenide by ion implantation.
The high-frequency limit of semiconductor devices of the above-described type is mainly limited by the mobility or drift velocity of the charge carriers in the semiconductor material, and the length of the channel. Thus, assuming a given geometry of the device, it is desirable to increase the mobility of the charge carrier. One known solution for this task is to use other compound semiconductors than gallium arsenide, as InP or Ga.sub.x In.sub.1-x P.sub.y As.sub.1-y which have higher carrier mobilities than gallium arsenide.
A factor which limits the mobility of the charge carrier in semiconductor devices of the above-identified type and which is independent of the type of semiconductor material used, is the large number of charged impurities in the current-carrying channel.